This invention relates generally to a controllable feeder for thin wire, and more particularly to a precision wire feeder for small diameter wire, particularly for welding operations.
High-energy density welding (HEDW) processes (i.e., electron beam and laser beam) are normally used autogenuously, without filler metal. However, the use of a filler wire is desirable when the geometry of a weld joint and an inherent gap or mismatch at the joint requires the use of a filler to provide joint closure or the desired weld geometry, or when the chemistry of the base metals is such that a filler metal is needed to adjust the chemical composition so that a crack-free weld can be attained.
U.S. Pat. No. 4,333,594 of E. Cloos discloses a prior art welding wire feeder having opposed planet guide rollers to drive a weld wire that is fed between the rollers.
U.S. Pat. No. 4,160,151 of P. Tonita discloses another welding wire feeder using opposed power driven wheels to drive the wire therebetween.
A synopsis of various drive mechanisms is provided by K. Brown, "Wire drive mechanisms", Metal Construction and British Welding Journal, Sept. 1969, page 407-412. One of these systems, the rotary wedge, is discussed in detail by K. Brown, "Fine wire feeder for microplasma welding", Metal Construction and British Welding Journal, Apr. 1969, pages 169-173.
The evolution of the rotary wedge, including a stepper motor drive, is discussed by K. Brown, "Wire feeders step out? Concept and prototype construction", The Welding Institute Research Bulletin, Jul. 1986, pages 223-228. The device discussed in this article uses a reserve loop between a constant speed capstan and a pulse driven capstan.
A wire feeder for HEDW processes must be capable of delivering a wire having a small diameter on the order of 0.25 mm (10 mils), or less, to a very small weld pool. The accurate, controlled, delivery of the free end of the wire to a precise location at a weld zone on a joint between adjacent pieces at a work station has been difficult to attain because of the obvious problems of kinking, breaking, and bending associated with this small wire. In addition, small diameter wire is notoriously difficult to accurately position.